To me, there are two types of investments. There are monetary investments and then there are investments of one's time and energy. For my newest book project, I asked 100+ people I consider mentors -- many of them modern giants in the tech space --what their most worthwhile investment they ever made was, either in terms of money, time or energy. Here are a few of my favorite responses:

Invest in reading.

"Every book I read that wasn’t assigned to me or that I didn’t read with a purpose in mind. The genuine love for reading itself, when cultivated, is a superpower. We live in the age of Alexandria, when every book and every piece of knowledge ever written down is a fingertip away. The means of learning are abundant — it’s the desire to learn that’s scarce. Cultivate that desire by reading what you want, not what you’re 'supposed to.'"

Giving unconditionally.

"Every time I’ve given with any expectation of return -- money, time, energy, whatever -- whenever I’ve expected something in return, the investment was stunted. Whenever I’ve given purely for giving, for helping, for supporting, for aiding, for encouraging -- with zero expectation or interest in any return whatsoever -- it’s been thoroughly fulfilling.

Most recently, my friend Krys was opening his own personal training gym. He’d just left his father’s business, money was tight and he was taking a big risk. I had full faith in him, I knew he would be great at it, and I wanted to remove some worry for him. So I paid his first year’s rent for him. No equity, no payback, no financial interest at all. It was just a gift. His business is thriving and it’s such a pleasure to see him and his young family (wife and two kids) so happy. I couldn’t be more thrilled for them."

Invest financially in yourself.

Kevin Kelly, co-founder of Wired Magazine, the All Species Foundation, a nonprofit aimed at cataloging and identifying every living species on Earth, and the Rosetta Project, which is building an archive of all documented human languages.

"I started my first business with $200. I bought an ad in the back of Rolling Stone magazine advertising a catalog of budget travel guides by mail for $1. Neither the catalog nor the book inventory existed. If I hadn’t gotten enough orders I would have returned the money [from any orders], but it all worked out by bootstrapping. I learned far more about business from that $200 than from a debt-inducing MBA."

Exercising regularly and being accountable to others.

“I had never been to the gym until around two years ago. This was partially laziness and partially intimidation. I don’t think there was a single breakthrough moment. I just had this realization: 'Am I going be the kind of guy who doesn’t exercise ever? Or not? And if the answer is ‘not,’ then why not right now?' That was the reasoning, but I didn’t have a medical crisis or anything. It’s one of the things that I always felt I was putting off. Then I went to the gym and realized I had no idea what to do. That’s why I got a trainer and invested in them for a year. I just went to the gym and asked, 'Do you have any trainers?' I didn’t put a lot of thought into the person, but the benefit was that, once it was scheduled and I was paying for it, it became harder to not go than to go.

It was a sunk cost, and there was a person who I’d have to text and say, 'I’m not going to show up,' which is a different type of accountability. That helped me to get over the initial hump of starting an exercise routine. If regular exercise could be bottled, it would be a miracle drug. Basically, everything in your life gets better if you find time to exercise regularly.

I feel like a lot of people in Silicon Valley serialize their lives. They think, 'First I’ll do college. Then I’ll do a startup. Then I’ll make money. Then I’ll do X.' There’s some truth in that [approach], but most of the most important stuff has to be parallel-processed, like your relationships and your health, because you can’t make up the time by doing more of it later. You can’t neglect your wife for four years and then say, 'Okay, now it’s my wife years.' Relationships don’t work that way, and neither does your health or your fitness...Figuring out a system, so that the stuff you need to do all the time happens, even while you might be placing disproportionate focus on one thing, is pretty important. Otherwise, you’ll be setting yourself up to be lonely and unhealthy in your future."

New month resolutions.

Ryan Shea, co-created Blockstack, a new decentralized Internet where users control their data, and apps run without remote servers.

"In 2016, I started doing New Month Resolutions [as opposed to New Year Resolutions]. Here’s some of what I did:

July: Daily reading

August: No TV or movies

September: No dairy

October: No gluten

November: Daily meditation

December: No news or social media feeds

As you can see, a few of the months were elimination months and a few were daily behavior months. The elimination months were interesting because I learned that I came away less dependent on the thing I eliminated. I now watch less TV and fewer movies, I eat less bread and gluten, and I still block the news and my social media feeds. The only thing I reinstated was dairy, choosing to continue to consume it.

The daily behavior months were interesting because they gave me an on- ramp to maintaining certain behaviors. I still meditate daily, and while I don’t read daily, I read at a frequency close to that. So far, my favorite experiments have been no news or social media feeds, workouts every day, no TV or movies, reading every day, and waking up at 7:30 every morning."